Tumor-induced angiogenesis plays a central role in the progression of tumors to malignancy, provides the critical transport of blood-born therapies into the tumor space, and supplies oxygen to effectuate oxygen-dependent radiological and light-based therapies. Pre-clinical research in tumor angiogenesis and tumor microvascular function has traditionally relied on histological methods, which suffer from well-known limitations, or fluorescence-based confocal and multiphoton microscopy, which provide high- resolution three-dimensional mapping of multiple parameters but support imaging over limited fields of view and depths of penetration. By contrast, optical coherence tomography approaches support a relatively larger field of view and depth of penetration and have the potential, if translated into the biological laboratory, to reveal critical and previously hidden aspects of the tumor microvasculature. In our laboratory, we have demonstrated the principles of a unique preclinical optical imaging technology that will be a powerful tool for investigating blood vessels and the biological microenvironment in vivo. The technology, optical frequency domain angiography (OFDA), supports high- resolution three-dimensional imaging similar to multiphoton and confocal microscopy. In this proposal, we propose optical, engineering, computational, and software solutions that will be required to realize a practical and robust OFDA instrument for translation into the biological laboratory. Our approach will unite investigators and resources at the Massachusetts General Hospital (MGH) and Physical Sciences, Incorporated (PSI). Innovations to the OFDA instrumentation and core algorithms will be performed by the MGH team, while construction of the computational hardware and software that is needed to improve processing will be performed by the PSI team. Our goal is to move OFDA technology from the engineering to the biological laboratory, which may catalyze research into basic cancer biology and cancer therapeutics.